Process for the manufacture of mercaptothiazolines



Patented May 16, 1944 PA O IC 6- Claims. (01. 260-302) a This invention relates to an improved process for the manufacture of certain heterocycliccompounds and has particular reference to the prep; aration ofv mercaptothiazolines.- These, com: pounds are of value as accelerators for the vulcanizationof rubber.- I c .-f

An object of the invention is to provide a process for the manufacture of lmercaptothiazolines which is adaptedto economical commercial'production. A further object is to provide a simple, easily controlled process whereby mercaptothiazolines may. be prepared in high yields. o These objects are attained by rnaking use of a new typeofreactionin which a cyclic alkyleneimine and carbon disulfide are reacted. in the presence of acaustic alkali to form a mercaptothiazoline. r

According toa preferred embodiment of my invention, ethyleneimine and carbondisulfide. are heated together in the presence. of; acaustic alkali. Theiollowing equation. represents the re action as itis believed to :take place. I

v H C-N H:CNH Haz 2052 NaOH *"c sn NaSH o'os 1 i 1;, 1" A method describedpin thevliterature provides for reacting ethyleneimine and carbon disulfide in the presence of ether., The chief. product of this;reaction,-a yellow oil, upon further treatment yields a small; amount of 2+mercaptothiazoline. I have discovered that remarkably-improved results are. obtained whenthe reaction is carried out in the presence of .aqueous caustic alkali. Under such-conditions, the lowyield obtained in aration of like compounds containing the five membered thiazoline ring and represented by the following formula v as well as the preparation of the six membered penthiazo'line ring, as shown by the following formula;

thedescribed method is increased to 90% of 2- mercaptothiazoline of high-purity. This unexpected result is due to the fact. that in the presence of caustic alkali essentially all of the ethyleneimine present reacts to ;.form; 2-mercapto,- thiazoline. In the absence of caustic alkali,,the usual reaction is fortwo molecular proportions of ethyleneimine to react with one molecular proportion of carbon disulfide to form a yellow oil. This oil is believed to be an ester, 2-aminoethylthiazolinyl sulfide. This compound is stable and does not decompose to form 2-mercaptothiazoline. When ethyleneimine is slowly added to an excess of carbon disulfide in certain organic solvents, a reaction in equi-m-olecular proportions occurs. The product of such a reaction is an unstable solid which is not z-mercaptothiazoline.

My process is not limited to the preparation of mercaptothiazoline itself but includes the prep- Kim each case representslike or unlike radicals whichmay ,be hydrogen or hydrocarbon groups such as alkyl, aryl, cycloalkyl,.aralkyl, etc. Water is, a very sattisfactory reactio diluent from which the mercapto bodiesdformed, are readily recovered because of their low water solubility. An organic solvent such as alcohol may also be employed The recovery of the product is somewhat'more involved where an organic solvent is used. l. I :In addition to ethyleneimine, C-alkylatedpr arylated, cyclic alkyleneimines, maybe employed in myprocess. Examples of such imines are methyl, ethyleneimine, ethyl ethyleneimine, amyl ethyleneimine, ,2-methyl S-phenylethyleneimine, 2,2-dimethyl ethyleneimine, 2,3-dimethylethyleneimine, 2,2-diphenylethyleneimine, tolyl ethyleneimine, 2,3-diphenylethyleneimine, and tri-v methyleneimine as well as its C-alkylated or arylatedderivatives. c i -,-..,The reactionis preferably carried out in a re-. actor provided with an agitator, a reflux condenser and a device for varying the temperature of the reaction mixture such as a jacket for circulating steam or cold water.

One molecular proportion of caustic alkali such as sodium or potassium hydroxide is dissolved in water, a ten percent solution being a convenient concentration for the reaction. Two molecular proportions of carbon disulfide are added. While agitating vigorously, a concentrated solution of one molecular proportion of ethyleneimine is slowly added, cooling usually being necessary to maintain a temperature of about C. When the addition of the imine has been completed, the reaction mixture is allowed to reflux gently until the carbon disulfide has all been consumed. The temperature is then increased to 100 andrefluxing continued until the reaction is}. complete, usually from one to three hours. After cooling, the solution often contains crystals of-2-mercaptothiazoline. The reaction mixture is acidified as for example with hydrochloric acid or sulfuric acid, whereuponlthe product is precipitated. The 2-mercaptothiazoline is filtered off, washed and dried at room temperature.

A small amount of wetting or dispersing agent is helpful in improving the dispersion of carbon disulfide i aqueous caustic alkali. Yields are much lower when less than two molecular proportions of carbon disulfide are used. The amount of caustic alkali may be increased to as much as three molecular proportions without much eiTect upon the yield, although there isno advantage in using more than onemolecular proportion.

The following example describes the process more specifically but it will be understood that the invention is not limited to these details.

Example. parts by weight of sodium hydroxide are dissolved in 400 parts of water in a reaction vessel provided with an agitator, a thermometer, and a reflux condenser. 168 parts of carbon disulfide are added. With vigorous agitation, a solution of 43 parts of ethyleneimine dissolved in parts of water is added in a very slow stream, while maintaininga temperature of about 30 C. The yellow solution obtained as a result of the reaction is refluxed for one hour and is then cooled. A small'amount of 2-mercaptothiazoline crystallizes out at this time. The reaction mixture is neutralized with hydrochloric acid whereupon the product is precipitated. The Z-mercaptothiazoline is filtered 01f, washed and dried at room temperature. The dry weight is 107.6-parts representing a 90.41% yield. The meltin'g'point is 100-1039'C.

From the data herein presented, the fact. will be readilyapparentthat this invention constitutes an economical method: for producing. mercaptothiazolines. 1 i

The process according'to this invention is quite distinct from a previously described methodin that my process is carried out in the presence'of caustic alkalil Caustic alkali influences the reaction in a manner suchthat the cyclicalk-ylene imine is converted almost quantitatively to amercaptothiazoline. A-similar reaction-in-the absence of alkali produces-only low yields of mercaptothiazolines,- the chiefproduct being presumably Z-amino-ethyl thiazolinyl sulfide. My process may be carried-outin standard equipment, requires but a short reaction period-and iseasily controlled, As the reaction is carriedout-inwater, inorganic. salts formed during the reaction and as a result of the neutralization, are eliminated with the filtrate.

I claim:

1. A process for producing a heterocyclic mercapto compound embodying a ring consisting of from three to four carbon atoms, one nitrogen atom and one sulfur atom, one carbonatom of said ring being directly between'the nitrogen and sulfur atoms and. joined to the sulfur of the nonnuclear mercapto group, which comprises interacting. one molecular proportion of a free, three to four membered, cyclic, alkylene imine and substantially two molecularproportions of carbon disulfide intlie presence of at least one molecular proportion of aqueous caustic alkali, and heating the reaction mixture to a temperatureat least as high as the atmospheric pressure refluxing temperature.

2. A process for producing a mercaptothiazoline which comprises interacting one molecular proportion of a free, cyclic, ethylene imine and at leastt'wo molecular proportionsof carbon-disulfide in the presence'of at least one molecular proportion of" aqueous caustic alkali, and heating the reaction mixture to a temperature at'le'ast as high as the atmospheric pressure refluxing temperature.

3. A process for producing a mercaptothia'zoline which comprises interacting substantially one molecular proportion of a free cyclic, ethylene imine and substantially two molecular proportions of carbondisulfide in'the presence of substantial lyone molecular proportion of aqueous caustic alkali, andheating the reaction mixture at 'a' tem- Derature not'less than about100 c proportions of carbon disulfidetin-the preseme,

of atleast one molecularproportion of'a caustic alkali, and heatingithe reaction mixture to a tein perature at least. as high. as theatmospher ic pressure refluxing:temperature.-' W I 6'. Alprocessfonproducing 2-mercaptothiazolin'e which comprises: interacting substantially one molecular.- proportion of free:-ethylene'r-imin'e and substantially. two: molecular proportions o'f c'ar bon disulfide in the presence of substantially-one molecularproportionofaqueoussodiumhydroxide and.v heating the reaction mixture at least as high aszthe atmospheric pressure-refluxing tempera ture. ROGER A 

